This invention relates generally to ink jet printing devices. In particular, the present invention is an inkjet cartridge including an ink level sensing mechanism having a pair of spaced electrical probes, wherein a change in electrical resistance measured between the electrical probes provides a reliable and accurate indication of a low ink condition in the ink reservoir of the ink container.
Ink jet printing systems frequently make use of an ink jet printhead mounted within a carriage that is moved back and forth across print media, such as paper. As the printhead is moved across the print media, a control system activates the printhead to deposit or eject ink droplets onto the print media to form images and text. Ink is provided to the printhead by a supply of ink that is either carried by the carriage or mounted to the printing system such that the supply of ink does not move with the carriage. For the case where the ink supply is not carried with the carriage, the ink supply can be in fluid communication with the printhead to replenish the printhead or the printhead can be intermittently connected with the ink supply by positioning the printhead proximate to a filling station to which the ink supply is connected whereupon the printhead is replenished with ink from the refilling station.
For the case where the ink supply is carried with the carriage, the ink supply may be integral with the printhead whereupon the entire printhead and ink supply is replaced when ink is exhausted. Alternatively, the ink supply can be carried with the carriage and be separately replaceable from the printhead or drop ejection portion.
Regardless of where the supply of ink is located within the printing system, it is critical that the printhead be prevented from operating when the supply of ink is exhausted. Operation of the printhead once the supply of ink is exhausted results in poor print quality, printhead reliability problems, and, if operated for a sufficiently long time without a supply of ink, can cause catastrophic failure of the printhead. This catastrophic failure results in permanent damage to the printhead. In addition to preserving the functional integrity of the printing system, many applications, and sometimes users, need to know in advance if the ink supply is getting low. Typically, unattended printing applications, as in kiosks, have such needs. Attended business applications also commonly need to know if the ink supply is getting low, such that the ink supply, or ink cartridge, can be replenished before it actually runs out of ink. Therefore, it is important that the printing system be capable of reliably identifying a condition in which the ink supply is nearly or completely exhausted. In addition, the identification of the condition of a nearly or completely exhausted ink supply should be accurate, reliable, and relatively low cost, thereby tending to reduce the cost of the ink supply and the printing system.
One type of ink container including a capillary reservoir with an ink level sensor is disclosed in the U.S. Pat. No. 5,079,570 to Mohr et al. entitled xe2x80x9cCapillary Reservoir Binary Ink Level Sensorxe2x80x9d which is assigned to the same assignee as the instant application and which is incorporated herein in its entirety by reference thereto. Mohr et al. is directed to an ink container that includes a housing within which is provided a capillary reservoir for storing a quantity of ink. The capillary reservoir has stippling where there is ink and no stippling where there is no ink. On one end of the ink container housing is an ink outlet. An ink level sensor is provided on one surface of the ink container housing. The ink level sensor comprises a C-shaped, transparent, ink level sensing tube with a first or upper port a first distance above the ink outlet and a second or lower port a shorter distance above the ink outlet. Both the upper and lower ports are ported through the ink container housing to the capillary reservoir.
In operation, as long as the ink level is above the upper port, the C-shaped tube of the ink level sensor is full of ink and is in static equilibrium. However, when the ink level reaches the upper port, the ink is sucked from the C-shaped tube of the ink level sensor and into the capillary reservoir due to an imbalance in the capillary pressures at the ink/air interfaces between the capillary reservoir and the upper port. The resulting sudden (i.e., instantaneous) depletion of ink in the C-shaped tube of the ink level sensor provides an almost instantaneous binary fluid level indicator. Since the C-shaped tube of the ink level sensor is transparent, a light detecting sensing device positioned adjacent to the C-shaped tube, can detect when the tube is empty (i.e., detect the binary fluid level indicator), whereupon the printing system can notify a user of the low ink condition of the ink reservoir of the ink container.
Although the above described binary ink level sensor provides a reliable and accurate indication of a low ink level within the ink reservoir of the ink container, there are some drawbacks to this ink level sensing system. One drawback concerns the use of the transparent C-shaped tube. This C-shaped tube is somewhat fragile, and because this tube extends out away from the housing of the ink container, it is somewhat susceptible to inadvertent damage during handling of the ink container. Damage to this tube may affect the overall operation and accuracy of the ink level sensing system and may result in unwanted ink leakage from the ink container. Moreover, because the C-shaped tube extends out away from the housing of the ink container, it can become soiled during handling of the ink container by a user. If this soiling is severe it may adversely affect the ability of the light detecting sensing device to detect when the C-shaped tube has become depleted of ink, thereby adversely affecting the overall operation and ability of the ink level sensing system of the printer to detect and warn a user of a low ink condition within the ink container.
As such, there is a need for an ink container employing an ink level sensing mechanism that allows a printing system to reliably and accurately determine the ink level within an ink reservoir of the ink container. The ink level sensing mechanism of the ink container should provide an accurate indication of a low ink level within the ink container, and should not be easily soiled or susceptible to damage during routine handling by a user. Lastly, the ink container should be relatively easy and inexpensive to manufacture.
In an embodiment, the present invention is a replaceable ink container for providing ink to a printhead of a printing system. The ink container includes an ink reservoir for containing a supply of ink, and an ink level sensor for determining an amount of ink in the ink reservoir. The ink reservoir includes a capillary ink storage member. The ink level sensor includes first and second resistance probes in fluid communication with the supply of ink and free from contact with the capillary ink storage member. A change in electrical resistance measured across the first and second probes indicates the amount of ink in the ink reservoir.